Never ending query in SQL Server 2012 - sql-server

Question

SQL Server 2012, Amazon RDS
This is my simple query
update [dbo].[DeliveryPlan]
set [Amount] = dp.Amount +
case when #useAmountColumn = 1 and dbo.ConvertToInt(bs.Amount) > 0
then dbo.ConvertToInt(bs.Amount)
else #amount
end
from
BaseSpecification bs
join
BaseSpecificationStatusType t on (StatusTypeID = t.StatusTypeID)
join
[DeliveryPlan] dp on (dp.BaseSpecificationID = bs.BaseSpecificationID and dp.ItemID = #itemID)
where
bs.BaseID = 130 and t.IsActive = 1
It can't be finished. If where condition bs.BaseID=130 (update 7000 rows) change for bs.BaseID=3 (update 1000000 rows) it lasts 13 sec.
Statistics are actual, I think
In performance monitor I see 5% processor usage
When I use sp to watch active connections and for this query
tempdb_allocations is 32, tembdb_current - 32, reads - 32 000 000, cpu - 860 000 (query lasts 20 minutes)
What is the problem?
UPDATE: I added non-clustered index for [DeliveryPlan] - by BaseSpecificationID + ItemID and problem is gone. Unfortunately I see this problem every day with different queries. And problem disappears unpredicatedly.

Answer 1

This will perform better and in a different way as the join conditions will narrow down the number of rows in the first go itself, rather than waiting for the where clause to execute. The execution plan will be different for both (with where/ without where).
UPDATE dp
SET Amount = dp.Amount + CASE
WHEN #useAmountColumn = 1
AND dbo.ConvertToInt( bs.Amount ) > 0 THEN dbo.ConvertToInt( bs.Amount )
ELSE #amount
END
FROM BaseSpecification bs
JOIN BaseSpecificationStatusType t ON
( bs.StatusTypeID = t.StatusTypeID
AND bs.BaseID = 130
AND t.IsActive = 1
)
JOIN DeliveryPlan dp ON
( dp.BaseSpecificationID = bs.BaseSpecificationID
AND dp.ItemID = #itemID
);

Answer 2

You may suffer from a locking condition for your base tables.
Optimize your query to update dp directly to avoid update all rows of DeliveryPlan
update dp set [Amount] = dp.Amount +
case
when #useAmountColumn=1 and dbo.ConvertToInt(bs.Amount)>0 then
dbo.ConvertToInt(bs.Amount)
else #amount
end
from
BaseSpecification bs
join BaseSpecificationStatusType t on (bs.StatusTypeID = t.StatusTypeID)
join [DeliveryPlan] dp on (dp.BaseSpecificationID = bs.BaseSpecificationID)
where
bs.BaseID = 130
and t.IsActive = 1
and dp.ItemID = #itemID

Answer 3

If the problem mentioned in the update part is that it comes and goes randomly, it sounds like bad parameter sniffing. When the problem happens you could look into plan cache to check if the query plan looks ok and in case it doesn't, what are the values the plan was created with (you can find them in the leftmost object in the plan) and for example use sp_recompile and see what kind of plan you'll get the next time.